<header>
  <h1>angular demo</h1>
</header>
<div class="container">
  <nav>
    <ul>
      <li><a routerLink="button">button</a></li>
      <li><a routerLink="tree">tree</a></li>
    </ul>
  </nav>
  <main>
    <router-outlet></router-outlet>
  </main>
</div>
<footer>
  <h4>&copy; 2025 . All Rights Reserved.</h4>
</footer>
